(1) Field of the Invention
This invention relates to filament wound pressure vessels for containing cryogenic fluid for use in refrigerated transport containers.
(2) Description of the Prior Art
Filament wound pressure vessels have a greater capacity to weight ratio than solid wall vessels. This advantage has resulted in the use of such vessels on space craft by NASA. However, the dissimilarity of the inner liner, typically metal, and the outer windings, typically resin-coated fiberglass, caused unequal stresses on the inner liner and winding that resulted in failure of the vessel after repeated use.
Before filing this application, a search was made in the United States Patent and Trademark Office. That search revealed the following United States patents:
______________________________________ GORCEY 3,137,405 BLUCK 3,210,228 BARTHEL 3,341,052 BARTHEL 3,504,820 MORSE ET AL 3,843,010 JACOBS 3,908,851 BROOK ET AL 4,073,400 GROVER ET AL 4,369,894 ______________________________________
These patents are specifically referenced because applicant believes the Examiner would consider anything revealed by a search to be relevant and pertinent to the examination of this application.
As applicant understands some of the above cited patents and the state of the prior art, workers in the art have solved some of the problems inherent in filament wound pressure vessels by using certain materials for the inner liner having desired strain characteristics in relation to the fiberglass windings. For example, BROOK ET AL specify certain alloys for the inner liner as possessing the desired strain characteristics of deforming elastically and being resistant to fatigue damage when cyclic strains are applied. GROVER ET AL discloses the elimination of laminate voids in the windings and allowing the metal inner liner to exceed its elastic limit to deform plastically. MORSE ET AL also discloses allowing the metal liner to exceed its elastic strain limit to deform plastically. However, MORSE ET AL provides a winding material having a greater elastic strain limit to withstand cyclic pressurizations and depressurizations although the elastic strain limit of the inner liner is repeatedly exceeded. As applicant understands his disclosure, GORCEY removes strain on the inner liner by pressurizing both sides of the metal liner with a pressurized bladder between the liner and the outer windings.
The references disclosed by the search apparently do not address another problem inherent in the use of filament wound pressure vessels to contain cryogenic fluids. Normally aluminum was used as the liner material to reduce weight. The storage of cryogenic fluids in filament wound pressure vessels can result in vessel temperatures colder than -190.degree. F. As the pressure vessel is cooled from ambient temperatures of about 70.degree. F., down to the cryogenic temperatures, aluminum liners tend to contract more than the winding material, causing the liner to separate from the windings. This separation results in the inner liner alone bearing the full force of the fluid pressure.
Before my invention, some workers in the art accounted for this problem with aluminum inner liners by first prestressing the aluminum liner until it deformed plastically, then winding the aluminum liner with the filament windings. Then as the pressure vessel was cooled to cryogenic temperatures, the filament windings and the inner liner contracted with the inner liner in compression and the windings in tension to keep the inner liner in contact with the windings.